pyjamas/pyjama/for/without for/IELTS/The IELTS

[Silverobama]

Question 1):

The following sentence was written by a native speaker based on what I said to them:

One thing which is interesting but strange is that people like wearing their pyjamas outdoors.

Context: Right here in Chongqing, many people like going out wearing a pyjama instead of their regular outfit.

My question: is it wrong to use "pyjamas" here? Should I use "pyjama"? Is there a grammar rule for this plural+singular structure?

Question 2):

I need to sign up for it at least a week in advance, and then wait for another two weeks for the results.

Context: I was talking about the IELTS test with a friend of mine. Is the "for" needed or optional or wrong?

Question 3):

How's it going with your preparation for IELTS?

Do I need to say "How's it going with your preparation for the IELTS" and why?

 

[tedmc]

1. "Pyjamas always comes with an "s", as in "trousers".

2. The preposition "for" after "wait" is optional.

3. IELTS acts like a proper noun, hence "the" is not required.

 

[emsr2d2]

You can say "pyjamas" or "a pair of pyjamas" but never "[a] pyjama".

 

[Silverobama]

You can say "pyjamas" or "a pair of pyjamas" but never "[a] pyjama".

May I have your opinions about the second and third question?

I notice that people do say “the IELTS”.

When are you planning to do the IELTS test and what is your target score in the reading section?

 

[Rover_KE]

May I have your opinions about the second and third questions?
.

Unrelated questions should be asked in separate threads.

NOTE: BE pyjamas = AE pajamas

'Py(a)jama is used adjectivally: I like to wear pyjama tops with tracksuit bottoms.